Research of Cassandra Michelle Kelleher, MD

Factors controlling lung alveolarization

Several important pulmonary diseases in newborns and infants are associated with significant morbidity and mortality due to lung hypoplasia from impaired alveolar development. These include congenital diaphragmatic hernia, cystic lung lesions, and the more common bronchopulmonary dysplasia. The current therapeutic algorithm for these diseases is supportive care aimed at minimizing complications and surgery when warranted. There are few treatments that target the cause of morbidity in these diseases, aberrant alveolarization. The goal of our research is to understand the factors controlling lung alveolarization and to identify therapies to enhance alveolar formation in neonates.

Alveolarization is the latest stage in lung development and occurs in humans from 36 weeks gestational age until adolescence. A human neonate is born with 50 million alveoli that increase to 300 million alveoli by adulthood, with the majority forming in the first six months after birth during a period referred to as “bulk alveolarization”. This massive expansion of alveoli is accomplished by a phenomenon called ‘septation’ during which protrusions from airway walls (septae) divide the distal airspace into alveoli leading to an exponential increase in the gas exchange surface of the lung.

The current lack of in vitro model systems of alveolarization greatly limits the identification and evaluation of therapies aimed at improving lung development. Therefore, to study the mechanisms of normal alveolar development, we have developed a mouse lung slice organ culture model that allows us to study postnatal alveolar development. The system facilitates alveolar septation and cellular differentiation in cultured lung that recapitulates in vivo alveolarization (Figures 1&2). The cultured lung slices provide a platform for evaluation of molecular mechanisms involved in alveolarization. As proof of principal, we have shown that addition of a TGFß neutralizing antibody results in cultured lung slices recapitulating TGFß-3 knockout mouse hypoplastic lung phenotype. We are using this model to study other molecular pathways involved in lung alveolarization and to identify and test therapeutics to treat lung hypoplasia.

Figure 1. Cultured and in vivo lungs have similar histology. Four day old lungs grown in culture for 4 days (P4+4) compared to lungs from 4 day (P4) and 8 day (P8) old mice. Lungs in culture undergo intercurrent septa formation similar to lungs that remain in vivo (arrows).